全文获取类型
收费全文 | 297596篇 |
免费 | 1562篇 |
国内免费 | 324篇 |
专业分类
化学 | 136625篇 |
晶体学 | 4651篇 |
力学 | 16868篇 |
综合类 | 3篇 |
数学 | 41998篇 |
物理学 | 99337篇 |
出版年
2021年 | 3083篇 |
2020年 | 3412篇 |
2019年 | 4189篇 |
2018年 | 6224篇 |
2017年 | 6438篇 |
2016年 | 7937篇 |
2015年 | 3516篇 |
2014年 | 6871篇 |
2013年 | 12102篇 |
2012年 | 10106篇 |
2011年 | 11772篇 |
2010年 | 9969篇 |
2009年 | 10125篇 |
2008年 | 11394篇 |
2007年 | 11187篇 |
2006年 | 9960篇 |
2005年 | 8593篇 |
2004年 | 8348篇 |
2003年 | 7758篇 |
2002年 | 8046篇 |
2001年 | 7661篇 |
2000年 | 6055篇 |
1999年 | 4486篇 |
1998年 | 4262篇 |
1997年 | 4122篇 |
1996年 | 3733篇 |
1995年 | 3296篇 |
1994年 | 3358篇 |
1993年 | 3374篇 |
1992年 | 3379篇 |
1991年 | 3786篇 |
1990年 | 3787篇 |
1989年 | 3794篇 |
1988年 | 3545篇 |
1987年 | 3628篇 |
1986年 | 3320篇 |
1985年 | 3850篇 |
1984年 | 4083篇 |
1983年 | 3488篇 |
1982年 | 3686篇 |
1981年 | 3372篇 |
1980年 | 3132篇 |
1979年 | 3621篇 |
1978年 | 3686篇 |
1977年 | 3855篇 |
1976年 | 3928篇 |
1975年 | 3671篇 |
1974年 | 3527篇 |
1973年 | 3688篇 |
1972年 | 3177篇 |
排序方式: 共有10000条查询结果,搜索用时 40 毫秒
341.
Nikolaos V. Tsekos Michael Garwood Kmil Ugurbil 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,156(2):187
A new technique is presented for generating myocardial tagging using the signal intensity minima of the transition zones between the bands of 0° and 360° rotations, induced by a tandem of two adiabatic delays alternating with nutations for tailored excitation (DANTE) inversion sequences. With this approach, the underlying matrix corresponds to magnetization that has experienced 0° or 360° rotations. The DANTE sequences were implemented from adiabatic parent pulses for insensitivity of the underlying matrix to B1 inhomogeneity. The performance of the proposed tagging technique is demonstrated theoretically with computer simulations and experimentally on phantom and on the canine heart, using a surface coil for both RF transmission and signal reception. The simulations and the experimental data demonstrated uniform grid contrast and sharp tagging profiles over a twofold variation of the B1 field magnitude. 相似文献
342.
The influence of interatomic distances on magnetic ordering in RMnSi compounds (R=La, Y, Sm, and Gd)
S. A. Nikitin T. I. Ivanova Yu. A. Ovchenkova M. V. Maslennikova G. S. Burkhanov O. D. Chistyakov 《Physics of the Solid State》2002,44(2):308-311
Magnetic ordering in the RMnSi (R=La, Y, Sm, and Gd) compounds is investigated. It is found that the type of magnetic ordering depends on the d Mn-Mn distance between manganese atoms inside the magnetic layers located in the planes perpendicular to the c axis. This inference is based on the results of studies performed with SmMnSi and GdMnSi compounds in which the distances between manganese atoms are close to the critical value d Mn-Mn that corresponds to the crossover between ferromagnetic and antiferromagnetic ordering in RMnSi compounds. The introduction of lanthanum and yttrium atoms into the rare-earth sublattice leads to an increase and a decrease in the unit cell size, respectively, and brings about magnetic phase transitions in the compounds under investigation. 相似文献
343.
344.
E. V. Kuz’min 《Physics of the Solid State》2002,44(6):1122-1129
The spin system of the Heisenberg model (s=1/2) on a square lattice with antiferromagnetic (AFM) exchange between nearest neighbors (in which there is no long-range magnetic order at any T≠0) is treated as a spatially homogeneous isotropic spin liquid. The double-time temperature Green’s function method is used in the framework of a second-step decoupling scheme. It is shown that, as T → 0, the spin liquid goes over (without any change in symmetry) to a singlet state with energy (per bond) ?0=?0.352 and the correlation length diverges as ξ ∝ T ?1 exp(T 0/T). The spatial spin correlators oscillate in sign with distance, as in the AFM state. The theory allows one to calculate the main characteristics of the system in all temperature ranges. 相似文献
345.
N. L. Dmitruk O. Yu. Borkovskaya R. V. Konakova I. B. Mamontova S. V. Mamykin D. I. Voitsikhovskiy 《Technical Physics》2002,47(6):698-702
The effect of 60Co gamma irradiation at doses of 103-2×105 Gy on the photoconversion and dark I-V characteristics of Au/GaAs surface-barrier solar cells (SCs) is studied. The morphology of the interface microrelief is varied
to reach the highest photoconversion efficiency. Of the two types of microrelief morphology (dendritic and quasi-grating)
obtained by the chemical anisotropic etching of n-(100)GaAs, the latter is more promising, particularly for SCs designed for space application, since the associated SCs offer
higher efficiency and radiation resistance. 相似文献
346.
347.
348.
Birational equivalence in the symplectic category 总被引:7,自引:0,他引:7
349.
The diffraction of plane surface gravitational waves by the edge of an ice cover lying on the surface of an incompressible fluid of infinitely great depth is considered. The ice cover is simulated by a thin elastic plate. The wave reflection and transmission coefficients are determined when it interacts with the ice cover. A wave field is constructed in the fluid under the conditions that a periodic lumped force and a lumped moment act on the edge of the ice cover. It is shown that as the incident wavelength increases the reflection coefficient tends to zero and the transmission coefficient tends to unity. 相似文献
350.